Effects of increased extracellular potassium on influx of sodium ions in cultured rat astroglia and neurons.
Membrane depolarization by elevated extracellular K+ concentration ([K+]o) causes rapid Na+ influx through voltage-sensitive Na+ channels into excitable cells. The consequent increases in intracellular Na+ concentration ([Na+]i) and/or [K+]o stimulate Na+,K+-ATPase activity, which in turn stimulates energy metabolism and rates of glucose utilization (CMR[glc]) in neurons. We previously reported that in cultured cells elevated [K+]o stimulated CMR(glc) in neurons but not astroglia; but increasing [Na+]i by opening voltage-sensitive Na+ channels with veratridine stimulated CMR(glc) in both. These results indicated that Na+ influx plays a key role in the regulation of energy metabolism in neurons and astroglia, but that depolarization of astroglial membranes by elevated [K+]o does not open voltage-sensitive Na+ channels as it does in neurons. To examine this possibility directly we have measured the effects of increased [K+]o and of veratridine on Na+ influx into cultured rat astroglia and neurons. Cells were incubated in bicarbonate buffer containing ouabain (1 mM), tracer amounts of 22NaCl, and various concentrations (5.4, 28, 56 mM) of K+ or 75 microM veratridine for 0-60 min. Cells were digested and assayed for intracellular 22Na+ content. Elevated extracellular K+ stimulated tetrodotoxin-sensitive 22Na+ accumulation in cultured neurons but inhibited 22Na+ influx in astroglia. Veratridine-stimulated Na+ influx in both astroglia and neurons (144% and 133%, respectively), and these effects were completely blocked by 10 microM tetrodotoxin. These results indicate that increased [K+]o does not open voltage-sensitive Na+ channels and may inhibit Na+ influx in astroglia.
Takahashi
S
S
Department of Neurology, Urawa Municipal Hospital, Saitama-ken, Japan.
Shibata
M
M
Fukuuchi
Y
Y
D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D008985:Monensin / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D012979:Sodium Radioisotopes; D014701:Veratridine / Q000494:pharmacology
D012979:Sodium Radioisotopes; D014701:Veratridine; D008985:Monensin; D012964:Sodium; D011188:Potassium